1. Field of the Invention
The present invention relates generally to communications methods and systems, and more particularly, to providing selections of operation modes of such communications systems.
2. Description of Related Art
A General Packet Radio System (“GPRS”) is a service that provides data packet communications for mobile Global system for Mobile Communications (GSM) and time-division multiple access (TDMA) users. In addition to GSM, GPRS also provides services to other digital cellular networks, such as DCS and PCS. As is known, GPRS uses this packet-mode technique to transfer high-speed and low-speed data and signaling in an efficient manner over GSM radio networks.
GPRS provides a variety of new and unique services to mobile wireless subscribers. For example, GPRS can maintain constant voice and data communications while mobile subscribers are in transit. Subscribers also are enabled to obtain connectivity whenever needed, regardless of location and without a lengthy login session. Via a GPRS mobile telephone, a subscriber can maintain an online connection while initiating a communication, without an overhead of setting up a data call. Finally, localization enables subscribers to obtain information that is relevant to their respective current locations. For example, GPRS enables location-based services that provide information about weather, traffic, restaurants, or retail stores, based on a subscriber's location at a particular moment in time.
FIG. 1 illustrates a basic architecture of a GPRS network 100 and a data transfer route in the GPRS network. The GPRS network attempts to reuse the existing GSM network element as much as possible. In order to effectively build a packet-based mobile cellular network, some new network elements, interfaces and protocols that handle packet traffic are also required. For example, the existing Mobile Station Switch Centers (“MSC's”) are based upon circuit-switched central-office technology and cannot handle packet traffic. Therefore, enabling GPRS on a GSM network requires the addition of two core modules, a Serving GPRS Service Node (“SGSN”) 110 and a Gateway GPRS Service Node (“GGSN”) 112, as shown in FIG. 1. GGSN 112 acts as a gateway between GPRS network 100 and an external IP network 114 such as an Internet or an x.25 Network, or another GPRS network (to facilitate GPRS roaming), and is connected with SGSN 110 via an IP-based GPRS backbone network 124. SGSN 110 is at the same level as MSC 118, and can be viewed as a “packet-switched MSC” (mobile station switch center). SGSN 110 provides packet routings to and from its service area for all MS's in that service area. SGSN 110 also detects new GPRS MS's in a given service area, processes registration of new MSs, and keeps a record of their respective locations inside the given area.
MS 102 is physical equipment used by the mobile subscribers, such as a mobile telephone or a laptop computer, which is GPRS-attached and can handle an enhanced air interface in GPRS network 100 and can packetize traffic directly. The GPRS-attached MSs may include a high-speed version of current telephones to support high-speed data access, a PDA (Personal Digital Assistant) device with an embedded GSM telephone, and PC cards for laptop computers. All MS's profiles are preserved in home location registers (“HLR”) 120 that are accessible by SGSN 110 and GSM MSC 118. A physical link (e.g., interface Gs) can be established and maintained between an MSC and a specific SGSN in each mobile network. The Gs interface allows the MSC to be aware of the status of a subscriber in the SGSN. The presence of the Gs interface facilitates combined signaling procedures from the MS.
SGSN 110 is also coupled to a BSC (Base Station Controller) 106 via a Frame Relay connection. BSC 106 manages radio resources including Base Transceiver Station (“BTS”) 104. BTS 104, is physical equipment, such as a radio tower, that is used to transmit radio frequencies over an air interface. The BSC 106 may be connected to several BTS's. Each BTS may serve more than one MS. The BSC and BTS, as a whole, are generally referred to as a BSS (Base Station System). To be utilized in the GPRS network, BSC 106 is linked to a Packet Control Unit (“PCU”) 108 that provides a physical and logical data interface out of the BSS for packet data traffic. PCU 108 converts packet data to/from SGSN 110 into a format that can be transferred to server 116/MS 102 and implements quality of service (QoS) measurements. For example, when either voice or data traffic is originated at the mobile subscriber, it is transported over the air interface to BTS 104, and from BTS 104 to BSC 106 in the same way as in a standard GSM call. However, at the output of BSC 106, the traffic is separated. Circuit-switched voice is sent to MSC 118 via circuit-switched channels (through interface A) per standard GSM, and data is sent to SGSN 110 via PCU 108 over the Frame Relay Interface (through interface Gb) and packet-switched signaling channels (through interface Gs).
Currently, the GPRS network can be designed to operate in three network operation modes (NOM1, NOM2, and NOM3), which are shown in FIGS. 2 and 3. The network operation mode of the GPRS network is indicated by a parameter transmitted in system information messages within a cell that dictates to a GPRS MS where to listen for paging messages and how to signal towards the core network. The network operation mode represents the capabilities of the GPRS network. In a NOM1 network, a MS can receive pages from the circuit switched domain (voice call) when engaged in a data call. The MS can suspend the data call or take both simultaneously, depending on the ability of the MS. In a NOM2 network, when engaged in a data call, pages may not be received from the circuit switched domain, since the MS is receiving data and not listening to the paging channel. In a NOM3 network, the MS can monitor pages from a CS network while receiving data and vice versa. However, it is very difficult to achieve in reality due to the processing power required.
There are also three classes of GPRS MS's, Class A, B, or C. These various GPRS MS's support various services. For example, a class A MS supports GPRS and other GSM services (such as SMS and voice) simultaneously, such that a class A MS can use circuit-switched voice and GPRS data services at the same time. A class B MS can monitor GSM and GPRS channels simultaneously, but can only support one of these service at one time. That is, the class B MS can simultaneously register circuit-switched voice and packet-switch data services but may only use one kind of service at a time. A class C MS supports either voice only or data only and thus cannot be simultaneously attached. The subscriber must select which service to connect to. Therefore, a class C MS can make or receive calls from only the manually (or default) selective service. The service that is not selected is not reachable. All classes of the MS's can operate in all network operation modes (NOM1, NOM2, and NOM3).
A GPRS MS, in either class, has three states: idle, standby, and active. Data is transmitted between a MS and the GPRS network only when the MS is in the active state because in the active state, the GPRS network knows the location of the MS and has an active connection. However, in the idle and standby state, the location of the MS is known only as to which cell (idle) or routing area (standby) it is in. (Each routing area may include more than one cell within a GSM location area.) Therefore, when the network wants to send a packet to a MS that is in the standby state, the MS must be paged. When the MS responds to the page from the BSS/SGSN, the SGSN now has an established connection and packets can be sent to the MS. When packets are sent/received (connection established), the MS is allocated in a Temporary Block Flow (TBF). When a TBF is allocated, this is the situation where paging coordination is required between the MSC and SGSN for circuit switched pages to be received.
FIG. 2 is a diagram showing the first network operation mode NOM1 of the GPRS network, in which GRPS MS 201 is attached to, through BSC 202, both SGSN 203 via interfaces Gb and Gs and to other GSM services through MSC 204 via interface A, and MS 201 supports simultaneous operation of GPRS and other GSM services. As shown, in NOM1, the network sends all paging messages for GRPS MS 201 either on a Common Control Channel (CCCH) or the GPRS paging channel or on a GRPS traffic channel (if a data transfer is in progress), such as interfaces Gs and Gb. MS 201 only needs to monitor one paging channel thus allowing it to “sleep” longer. Further, the paging load could be reduced since paging is performed on the routing area level.
FIG. 3 is a diagram illustrating the second and third network operation modes NOM2 and NOM3 of the GPRS network, in which GPRS MS 301 is attached to, through BSC 302, both SGSN 303 via interface Gb and other GSM services through MSC 304 via interface A and can only operate one set of services at a time. In NOM2, the network sends all paging messages for GPRS MS 301 out on the CCCH. The MS must monitor this channel even when allocated a GPRS data channel. In NOM3, the network sends out the CS paging for GPRS MS 301 on the CCCH, and GPRS paging out on a Packet Paging channel (PPCH). If PPCH are present in the cell, then MS 301 must monitor both the CCCH and the PPCH channels. The CS paging occurs at the Location Area level and the PS paging occurs at the cell or Routing Area level.
The primary difference between NOM1, NOM2 and NOM3 is that paging and signaling coordinate in NOM1 to occur between MSC 203 and SGSN 204. The primary difference between NOM2 and NOM3 is that in NOM 3, the GRPS MS 301 can be required to monitor different paging channels. NOM1 has two flavors, one with different paging channels for CS only and CS/PS combined pages (PPCH), and one with a single, common paging channel for use by both CS and PS pages.
Currently, the MS receives the network operation mode from system information transmitted within the cells. However, there is no coordination between each node (BSC, SGSN and MSC) that determines what operation mode the network can support. Since the network operation mode indicates how the MS signals and receives signals from the network, it is possible for the MS to perform or behave in a manner indicated by the received mode of operation, and for other nodes in the network to expect a different behavior. This can result in prolonged loss of service for the MS.
Accordingly, a communications system and method that provides more flexible communications service to MS subscribers is thus desirable.